Certain visual geometric proportions and ratios considered by some as metaphysically or aesthetically significant and evoking a pleasant response in an observer. These and other proportions and ratios may evoke an equivalent response when perceived aurally in musical consonances and harmonies.
Speculation on such relationships has led to the belief that certain ratios and proportions were intrinsically beautiful and were keys to understanding the relationship between microcosm and macrocosm and to revealing fundamental truths about the structure of the universe. The aesthetic qualities of the golden section and the golden rectangle have led to their extensive use in artistic and architectural products. Significance is attached to the numeric properties of the logarithmic spiral, its widespread occurrence in attractive natural forms, and its relevance for the structural understanding of growth.
Some kind of controlling or regulating system of proportion has been considered a desirable unifying and harmonizing device, although the more recent tendency is to reject the notion that one system of proportion, a priori, is better or more agreeable than another.